Encyclopedia / D / Diabetes


What Is Diabetes?

Diabetes mellitus is a metabolic disorder with abnormally high blood glucose levels (hyperglycemia) as its most prominent feature. During intestinal digestion, carbohydrates and proteins are broken down into simple sugars and amino acids, respectively. The liver converts all of the sugars and some of the amino acids into glucose, a simple sugar that is used for energy by every cell in the body.

Glucose passes from the bloodstream into the cells with the help of insulin, a hormone produced by the pancreas (a pear-shaped organ located just below the stomach). By attaching to receptor sites on the surface membrane of a cell, insulin promotes the movement of glucose-transport proteins from the interior of the cell to its surface, where they bind with glucose and carry it into the cell. In diabetes mellitus, several problems may interfere with this process: pancreatic insulin production may be partially or completely impaired, or body cells may become unable to respond to normal amounts of insulin efficiently.

These underlying problems in fact distinguish the two main types of diabetes. In type 1 diabetes mellitus, also known as juvenile-onset diabetes, the pancreas produces little or no insulin. Type 1 diabetes develops suddenly and most commonly affects those under age 30; the average age of onset is between 12 and 14. However, type 1 diabetes accounts for only about 5 percent of cases of diabetes mellitus. In the much more common type 2 diabetes mellitus, also known as adult-onset diabetes, insulin production by the pancreas is only moderately reduced, but cells are unable to respond efficiently to insulin—a condition referred to as insulin resistance. The onset of type 2 diabetes is usually gradual and tends to affect people over age 40, particularly those who are overweight. Infrequently, an adult may develop type 1 diabetes.

In both type 1 and type 2 diabetes, the hyperglycemia leads to excretion of glucose in the urine and an accompanying increase in urine production. If inadequate amounts of insulin are administered to patients with type 1 diabetes, unrestrained release of fatty acids from adipose (fat) tissue leads to the overproduction of ketone bodies in the liver. Accumulation of ketone bodies can cause a life-threatening condition known as diabetic ketoacidosis (DKA). DKA may occasionally affect those with type 2 diabetes in periods when the body is highly stressed—for example, during a severe infection.

People with type 2 diabetes are susceptible to another life-threatening condition known as a hyperosmolar nonketotic state, characterized by extremely high blood sugar levels. This condition usually occurs in elderly persons with some other serious underlying illness. An episode of either DKA or the hyperosmolar state may be the first indication that someone has diabetes.

People with diabetes may also suffer from low blood sugar (hypoglycemia) if too much insulin or oral hypoglycemic agent is given for treatment (see Hypoglycemia for more information).

Diabetes complications. After 10 to 20 years of diabetes, patients are at risk of developing complications, such as vision disorders, kidney damage, and peripheral nerve degeneration (neuropathy). Loss of sensation in the feet may allow injuries to go unchecked and become infected. In addition, people with diabetes are at increased risk for developing atherosclerosis—the buildup of plaques, which form in large arteries and act to narrow the arteries. Atherosclerosis can reduce blood flow to the heart, resulting in coronary heart disease and the risk of heart attack. It can also lead to stroke—people with diabetes are more than twice as likely to have a stroke as people without diabetes. If arteries supplying the legs are affected, the combination of foot infections and decreased blood supply can lead to gangrene (tissue death), which may require amputation.

Diabetes mellitus (and its complications) is the fourth leading cause of death in the United States. But strict control of blood glucose can delay or prevent these complications. Although there is no cure, almost all people with diabetes are able to control their symptoms and lead full, productive lives.

Who Gets Diabetes?

According to the American Diabetes Association, an estimated 29.1 million Americans have diabetes. This figure includes 208,000 children under age 20, most of whom have type 1 diabetes. About 11.8 million are adults over the age of 65 have diabetes, mostly type 2. Approximately 80% of people with type 2 diabetes are overweight or obese. African Americans, Hispanics, Asians, and Native Americans are at greater risk than whites of developing type 2 diabetes, though scientists aren’t sure of the reason for this. More than a third of people with diabetes have not had their condition diagnosed.

About 86 million Americans have prediabetes—signified by higher-than-normal glucose levels that are not in the diabetes range.


Note: Symptoms of type 1 diabetes develop quickly in most cases. With type 2 diabetes, symptoms gradually develop over time and may be mild in the early stages. Often type 2 diabetes is diagnosed during routine laboratory tests.

  • Excessive and frequent urination (as often as every hour or so). Nighttime awakening to urinate is common.
  • Increased thirst.
  • Increased appetite.
  • Unintentional weight loss.
  • Blurred vision.
  • Fatigue and weakness.
  • Recurring or persistent infections of the bladder, skin, or gums.
  • Numbness and tingling in feet and hands.
  • Symptoms of hypoglycemia: early signs include hunger, a tingling sensation in the hands, palpitations, profuse perspiration, shakiness, or weakness. (These symptoms may not occur in people with longstanding diabetes.) Extreme hypoglycemia can cause neurologic symptoms such as headache, double vision, slurred speech, numbness, and confusion.
  • Emergency symptoms of hyperosmolar nonketotic states: extreme thirst, lethargy, weakness, mental confusion, coma.
  • Emergency symptoms of diabetic ketoacidosis: nausea and vomiting, labored breathing, mental confusion, coma.

Causes/Risk Factors

  • Type 1 diabetes is an autoimmune disorder, resulting from a mistaken attack by the immune system on insulin-producing cells in the pancreas.
  • Genetic factors are important in type 2 diabetes.
  • Obesity is the major contributing factor for type 2 diabetes. The risk rises as a person’s weight increases.
  • Race and ethnic background affect diabetes risk.
  • Many people with prediabetes, if they avoid recommended lifestyle changes or medications, will develop type 2 diabetes.
  • Certain drugs, such as corticosteroids or thiazide diuretics, may increase the risk of type 2 diabetes.
  • Other disorders, such as hemochromatosis, chronic pancreatitis, Cushing’s syndrome, or acromegaly, may lead to diabetes. Surgical removal of the pancreas may also lead to diabetes.
  • Pregnant women may develop diabetes (gestational diabetes), which usually disappears after childbirth; these women are at an increased risk for subsequent development of type 2 diabetes.
  • Contrary to popular belief, eating lots of foods rich in sugar does not promote diabetes.


  • Patient history and physical examination may suggest presence of the disorder.
  • Diagnosis is made when fasting blood tests show high glucose levels (126 mg/dL or greater) on at least two occasions. Values of 100 to 125 mg/dL indicate prediabetes.
  • When test results are ambiguous, a glucose tolerance test may be done. A drink containing 75 grams of glucose is swallowed and blood glucose levels are measured every 30 minutes over a two-hour period.
  • Urine samples may be analyzed for protein content.
  • Blood glycohemoglobin is measured; it indicates the average blood glucose levels over the preceding two to three months.


Diabetes is a complicated disorder, and treating it should be individualized. The successful management of either type 1 or type 2 diabetes call for a personalized treatment plan that takes prior health problems, health habits and characteristics, and risk factors for other disorders into account. A primary care doctor can often direct a patient’s treatment plan. But treatment is usually improved by having a team of professionals who have specialized knowledge about various aspects of the disease. The team can include a diabetes nurse educator (who specializes in day-to-day management of diabetes), a dietitian for meal planning, a pharmacist, and specialists to check on eyes, kidneys, and feet. Below are areas of treatment that diabetes management covers.

For type 1 diabetes:

  • Daily injections of insulin are necessary. One to four daily injections are required to control blood glucose levels. Long-acting and rapid-acting insulin preparations are available; a combination of the two kinds is often prescribed. Some people with type 1 diabetes use insulin pumps and other delivery systems to achieve better blood sugar control and decrease the number of their injections.
  • A strict diet and schedule of meals are necessary to control blood glucose levels. Your doctor may recommend a diet low in fat, salt, and cholesterol, and may advise you to see a nutritionist for dietary planning.
  • Because both exercise and insulin lower glucose levels, exercise and insulin injections must be timed so that they do not combine to cause a dangerous drop in blood sugar (hypoglycemia).
  • Strict adherence to the timetable of injections, meals, and exercise is necessary for proper management of the disease.

For type 2 diabetes:

  • Losing excess weight—and maintaining weight loss—is important to improve blood glucose control; it will also help control risk factors, such as blood pressure and cholesterol, associated with cardiovascular disease. A diet low in fat and other calories, in addition to regular exercise, is necessary to control weight.
  • Bariatric (weight loss) surgery may be considered for very obese adults, especially those who have difficulty controlling their diabetes or associated medical problems.
  • If exercise and diet do not lower glucose levels sufficiently, oral drugs for the management of type 2 diabetes may be prescribed. (They may also be prescribed for those with type 1 diabetes who are insulin resistant.) The drugs—which work in various ways to help lower blood glucose—can be used singly or sometimes in combination.
  • Biguanides (metformin) lower blood glucose by curbing the amount of glucose produced in the liver. Metformin is generally considered the first line of treatment for type 2 diabetes unless the patient has an intolerance or a specific reason not to take it.
  • Sulfonylureas (chlorpropamide, glipizide, glyburide, glimepiride) stimulate the cells of the pancreas to release more insulin.
  • Meglitinides (repaglinide) also trigger the release of insulin by stimulating the pancreas.
  • Thiazolidinediones (pioglitazone, rosiglitazone) help insulin work better and lower glucose in the liver. Though widely used in recent years, the drugs have a number of side effects, including weight gain caused by fluid retention and also an increase in fat tissue. The use of rosiglitazone (Avandia) has been restricted because of concerns over increased heart attack risk.

. GLP-1 agonists (exenatide and liraglutide) boost the release of insulin after eating. These are long-acting forms of naturally occurring hormones which help maintain normal blood sugar, but which tend to lose their effectiveness in type 2 diabetes.

  • DPP-4 inhibitors (alogliptin, linagliptin, sitagliptin, saxagliptin), which are the newest diabetes drugs, help prolong the activity of hormones that boost the release of insulin after eating, leading to better glucose control without causing hypoglycemia (as can happen with sulfonylureas and meglitinides).
  • Insulin injections may be necessary in more severe cases of type 2 diabetes, or if a patient with type 2 diabetes contracts an additional illness. About 40% of people with type 2 diabetes eventually require some type of insulin treatment—often taken in combination with an oral medication—to control their blood glucose.

For both types of diabetes:

  • Blood tests to measure glucose levels should be performed as your doctor recommends, one to four times a day. Your doctor will recommend a blood monitoring device to use at home.
  • Excellent control of blood glucose levels delays or prevents late complications affecting the eyes, kidneys, and nerves. Additional steps, as noted below, can also reduce the risk of complications developing or worsening.
  • Careful attention must be paid to the risk factors for atherosclerosis because of its increased occurrence with diabetes. Those suffering from diabetes should not smoke, should reduce dietary saturated fat, cholesterol, and salt, and should take any medications prescribed for high blood pressure or high cholesterol levels. You should also talk to your doctor about taking a daily aspirin tablet to reduce the risk of blood clots.
  • People with diabetes should drink generous amounts of water when stricken with another illness, such as the flu, to replace lost fluid and prevent diabetic coma. When ill, people with type 1 diabetes should test their urine for ketones every four to six hours.
  • Patients with diabetes need an eye examination by an ophthalmologist at least once a year to detect the earliest manifestations of retinopathy—damage to the eye’s retina caused by changes in the tiny blood vessels that supply the retina. Retinopathy can be effectively treated with laser photocoagulation procedures to prevent the rupture of blood vessels—but only if retinopathy is detected early.
  • People with diabetes should practice good foot care and check their feet every day. Nerve damage from diabetes mellitus reduces sensation in the feet, and small foot problems may turn into major infections. Even the most minor cut or abrasion should be treated. Referral to a foot doctor (podiatrist) for treatment and periodic exams is often recommended.
  • Nerve damage (neuropathy) can involve loss of feeling in parts of the body other than feet, as well as a loss of reflexes and muscle control. It can also cause damage to body functions not under voluntary control—for example, erectile dysfunction in men. Medication is often needed to treat diabetic neuropathy.
  • About 30 to 40 percent of people with type 1 diabetes and 20 percent of those with type 2 diabetes eventually develop some kidney damage. Medication and dietary restrictions can help prevent or slow the progression of kidney damage. But if kidney function deteriorates to the point of kidney failure, dialysis, an artificial blood-filtering process, may be necessary. In advanced cases a kidney transplant may be advised.
  • Kidney damage can be slowed by controlling blood pressure and using ACE inhibitors.
  • The American Diabetes Association can provide information about support groups in your area.


  • To prevent the development of type 2 diabetes, lose weight if you are more than 20 percent overweight, and maintain weight within healthy limits.
  • Exercise regularly. Diet and exercise are the cornerstones of preventing type 2 diabetes.
  • There is no known way to prevent type 1 diabetes.
  • People with either type of diabetes should get regular eye examinations to aid in early detection and treatment of diabetes-related vision disorders.

When To Call Your Doctor

  • Call a doctor if you notice a sudden or gradual increase in hunger, thirst, and urine output.
  • Call a doctor if you have diabetes and an additional illness such as a cold or the flu causes blood sugar levels to go out of control. Do not take over-the-counter medications without first consulting your doctor.
  • Emergency Call an ambulance if a person with diabetes loses consciousness. Inform the doctor or the rescue worker that the person has diabetes.
  • Emergency (in type 2 diabetes) Call an ambulance immediately if you develop symptoms of a hyperosmolar nonketotic state; these include extreme thirst, lethargy, weakness, and mental confusion.
  • Emergency (in type 1 diabetes) Call an ambulance immediately if you develop symptoms of diabetic ketoacidosis; these include dry mouth, dry and flushed skin, sweet or fruity-smelling breath, labored breathing, vomiting, and abdominal pain, with or without excessive urination and extreme thirst.
  • Emergency (in type 1 diabetes) Call your doctor right away if urine tests detect the presence of ketones and the steps given by your doctor fail to control the problem.

Robert Hurd, M.D., American Board of Internal Medicine and Professor of Endocrinology and Health Care Ethics, Xavier University, Cincinnati, OH. Review provided by VeriMed Healthcare Network.